1. Field of the Invention
The present invention relates to a photoresist composition and a method of manufacturing a thin-film transistor substrate using the photoresist composition. More particularly, the present invention relates to a photoresist composition having a relatively high heat-resistance to reduce a profile variation of a photoresist film formed using the photoresist composition when heated, and a method of manufacturing a thin-film transistor substrate using the photoresist composition.
2. Description of the Related Art
In general, a liquid crystal display apparatus is manufactured through a five-mask process. However, a four-mask process has been developed in order to reduce manufacturing costs and to improve manufacturing efficiency. The four-mask process involves double etching a photoresist film. In the four-mask process, it is preferable that a profile of a photoresist film formed by coating a photoresist composition on a substrate be made relatively large in order to easily progress the four-mask process. When the photoresist film has a smaller profile, as when it is made relatively thin on the substrate, the four-mask process has less room for error as the first etching must be performed precisely to avoid excess removal of the photo resist film. When the profile of the photoresist film is relatively large, a design margin is reduced, and an etching process may be more easily performed. When a photoresist pattern formed from a conventional photoresist composition is heated at a temperature of no less than about 125° C., the photoresist pattern flows so that an angle between a side surface of the photoresist pattern and an upper surface of a substrate, on which the photoresist pattern is formed, becomes no more than about 40 degrees.
FIGS. 1A to 1D are scanning electronic microscope (“SEM”) pictures showing a photoresist pattern formed from a conventional photoresist composition flowing when baked.
Particularly, FIG. 1A is an SEM picture showing a process developing a photoresist pattern, and FIG. 1B is an SEM picture showing an initial profile of the photoresist pattern after being developed. An angle between a side surface of the photoresist pattern and an upper surface of a substrate, on which the photoresist pattern is formed, is about 50 degrees.
After the developing process, the photoresist pattern is post-baked and hard-baked in order to increase an etching-resistance of the photoresist pattern. When the photoresist pattern is heated it flows so that an angle between the side surface of the photoresist pattern and the upper surface of the substrate, on which the photoresist pattern is formed, decreases. The resulting angles become about 30 degrees to about 35 degrees.
FIG. 1C is an SEM picture showing the photoresist pattern after a hard-baking process, and FIG. 1D is an SEM picture showing a profile of the photoresist pattern which has reflown through a hard-baking process.
When the photoresist pattern reflows, a channel length between rises in the photoresist becomes narrower as shown in FIG. 1C. Thus, a time for etching is increased, and a skew is increased.
Furthermore, the photoresist pattern formed from a conventional photoresist composition is sensitive to a temperature variation of the equipment used in its manufacture so that a shape of the photoresist pattern depends on a temperature variation of the manufacturing apparatuses. Thus, a thickness variation of the photoresist pattern is increased so that a short circuit may be caused in an area where the photoresist pattern is relatively thick, and an open defect may be caused in an area where the photoresist pattern is relatively thin.